Method and apparatus for substrate handling and printing

ABSTRACT

An apparatus and method are described for transferring substrates to and from a printer. In a described embodiment, the apparatus includes a pair of storage units for vertically stacking substrates, and a laterally moveable platen. The storage units are moveable vertically with respect to the platen in order to transfer substrates to and from the platen. The apparatus and method have particular application in the handling and printing large numbers of biological samples on glass slides.

The present invention relates to the field of printing, and inparticular to the printing of large number of substrates.

Ink jet printheads can be used to position spots of liquids, for examplebiological samples, on substrates such as glass slides. An importantapplication-of this technique is the manufacture of DNA microarrays.

When manufacturing a microarray, it is normally required to print one,two, three or more spots of each liquid onto each of a large number(tens to hundreds) of substrates. Typically, there will be a very largenumber (hundreds to tens of thousands) of different liquids to beprinted onto the substrates, so the printing process may be lengthy.

The cleaning of the printhead before the introduction of the next set ofliquids takes time, and therefore the once a set of liquids has beenintroduced into the printhead, they should be printed onto all theslides before another set of liquids is loaded.

Patent application WO 02/11889 discloses a method whereby an ink jetprinthead having multiple chambers, each associated with a nozzle, canbe used to print multiple different liquids at the same time. Theprinting can be carried out without cross-contamination between theliquids, despite the fact that the chambers are connected by one or moremanifolds internal to the printhead. The liquids are introduced viacontiguous groups of nozzles into the associated chambers and printedbefore they have time to mix by diffusion. Handling multiple liquidstherefore offers the possibility of reducing the time taken to do theconsiderable amount of printing required in the production of DNAmicroarrays.

However, if a large number of slides is to be printed, their area is toolarge to allow them to be arranged in a plane -for easy access duringprinting. It is therefore only practical to arrange smaller groups ofthe slides for printing. Since the slides do not occupy much volume, itis convenient to store the slides in a multilayer stack. However, thetransfer into and out of storage inevitably occupies some time,conflicting with the need to minimise manufacturing time.

It would therefore be desirable to provide a method and apparatus forhandling and printing substrates that obviated or at least mitigatedsome of the drawbacks of conventional systems.

It is one aim of an aspect of the invention to provide a method forloading and unloading substrates to printing apparatus in an efficientand rapid manner.

It is a second aim of an aspect of the invention to provide apparatusfor loading and unloading substrates to printing apparatus in anefficient and rapid manner.

Further aims and objects of the invention will become apparent from areading of the description.

According to a first aspect of the invention, there is providedapparatus for transferring substrates to and from a printer, comprising:

-   -   a first storage unit for storing substrates prior to a printing        operation, the first storage unit having a plurality of        vertically stacked substrate supports;    -   a platen for receiving a substrate from said first storage unit,        aligning the substrate with a printhead prior to a printing        operation, and displacing the substrate subsequent to a printing        operation to an unloading position;    -   a second storage unit for storing substrates subsequent to said        printing operation, the second storage unit having a plurality        of vertically stacked substrate supports;    -   wherein the first and second storage units are movable        vertically with respect to the platen, and in use, relative        vertical movement of the first storage unit and the platen        transfers a substrate from the supports of the first storage        unit to the platen, and relative vertical movement of the second        storage unit and the platen transfers a substrate from the        platen to the supports of the second storage unit.

Preferably, the vertically stacked substrate supports of the first andsecond storage units are arranged to support substrate-handling traysfor holding a plurality of substrates.

Preferably, the platen receives a substrate-handling tray from the firststorage unit, the substrate being held on said substrate handling tray.

The substrate handling tray may extend lengthways across the width ofthe platen, the length of the tray being greater than the width of theplaten.

Preferably, the first and second storage units are frames defining aninterior cavity, into which the platen extends.

According to a second aspect of the invention, there is provided amethod for transferring substrates to and from a printer, comprising thesteps of:

-   -   imparting relative vertical movement between a first storage        unit for storing substrates and a platen, the first storage unit        having a plurality of vertically stacked substrate supports,        thereby transferring a substrate from the supports of the first        storage unit to the platen;    -   aligning the substrate with a printhead;    -   printing on the substrate;    -   displacing the substrate to an unloading position;    -   imparting relative vertical movement between a second storage        unit for storing substrates and the platen, the second storage        unit having a plurality of vertically stacked substrate        supports, thereby transferring a substrate from the platen to        the supports of the second storage unit.

According to a third aspect of the invention, there is provided a methodfor printing substrates on a platen, the method comprising the steps of:

-   -   printing a substrate by imparting linear movement to the        printhead, thereby causing the printhead to traverse the        substrate in a first direction, whilst simultaneously        transferring a further substrate between the platen and a        substrate storage unit;    -   aligning the second substrate tray with the printhead, whilst        reversing the direction of motion of the printhead;    -   printing the substrates held on a second substrate tray by        imparting linear movement to the printhead, thereby causing the        printhead to traverse the substrates in a second direction        opposite to the first.

Preferably, the transfer of a substrate between the platen and thesubstrate storage unit is carried out by imparting relative verticalmovement between a substrate storage unit and the platen, the storageunit having a plurality of vertically stacked substrate supports.

According to a fourth aspect of the invention, there is provided amethod for printing substrates on a platen, the method comprising thesteps of:

-   -   printing a substrate by imparting linear movement to the        printhead, thereby causing the printhead to traverse the        substrate in a first direction;    -   transferring a further substrate between the platen and a        substrate storage unit;    -   aligning the further substrate with the printhead, whilst        reversing the direction of motion of the printhead;    -   printing the substrates held on a second substrate tray by        imparting linear movement to the printhead, thereby causing the        printhead to traverse the substrates in a second direction        opposite to the first.

According to a fifth aspect of the invention, there is provided a methodfor printing substrates on a platen, the method comprising the steps of:

-   -   printing a substrate by imparting linear movement to the        printhead, thereby causing the printhead to traverse the        substrate in a first direction, whilst simultaneously        transferring a further substrate between the platen and a        substrate storage unit;    -   aligning the second substrate tray with the printhead;    -   reversing the direction of motion of the printhead;    -   printing the substrates held on a second substrate tray by        imparting linear movement to the printhead, thereby causing the        printhead to traverse the substrates in a second direction        opposite to the first.

Preferably, the steps of the method are repeated.

There will now be described, by way of example only, various embodimentsof the invention with reference to the following drawings, of which:

FIG. 1 is a plan view of apparatus according to an embodiment of theinvention;

FIG. 2 is a front view of the apparatus of FIG. 1;

FIG. 3 is a side view of the apparatus of FIG. 1;

FIG. 4 shows a side view of the apparatus and a table useful forexplaining a method in accordance with an embodiment of the invention;

FIG. 5 shows a table useful for explaining a method in accordance withan alternative embodiment of the invention.

Referring firstly to FIGS. 1 and 2, the apparatus generally depicted at10 includes a platen 12, four cages 13 a to 13 d, and a linear rail 14.Each cage is a rectangular metal frame 15 having a series of verticallystacked substrate supports in the form of inwardly protruding ledges 16.The cages are shaped to receive a number of slide trays 17, each slidetray holding a linear array of slides to be printed. Each slide tray 17is oriented lengthways across the width of the platen 12, and the lengthof the trays is greater than the width of the platen. The platen 12 istherefore able to extend into a central cavity defined by the frame ofthe cage. The platen 12 has four positions for receiving slide trays.Above one of the positions is a linear rail 14 along which the printhead19 can be moved in a reciprocating motion following a trapezoidalvelocity profile. The acceleration and deceleration associated with thechanging of direction of the printhead at each end occurs beyond the endof the trays. The printhead axis is positioned with two cages 13 oneither side. A suitable printhead is the XaarJet XJ126R.

The arrangement for the slides within a tray is a linear array of, say,twenty five slides 18 with their short edges parallel to the long axisof the trays and the long edges of adjacent slides facing one another.This minimises the time occupied travelling over each slide. Aconvenient pitch for the slides is 27 mm, which allows space formechanisms to hold the slides, and fits in with the possibility of usingtwo or more printheads, line astern. A printhead such as the XaarJetXJ126R can be set at a pitch of 54 mm, which works well with the 9 mmpitch of the well-plates from which the liquids are usually obtained.

As shown in FIG. 2 ledges 16 of the cages above the platen 12 are filledwith trays 17 (all but one shown in dotted lines for clarity), while theledges below are empty. The cage is shown in a position where it hasmoved downwards, so that the tray is brought into contact with theplaten. A slight further downward movement of the cage causes the trayto come to rest on the platen, freeing the trays from the ledges of thecage on which it was resting and depositing it onto the platen. Asubsequent fore-aft movement of the platen will carry the tray to aposition outside the frame of the cage.

FIG. 3 shows the four cages 13 a to 13 d from a side view. Cages 13 aand 13 c are loaded with slide trays (not shown), and are positionedabove the platen. In use, these upper cages will descend in stages fromthe high positions, depositing trays onto the platen in readiness forprinting. In contrast, cages 13 b and 13 d are empty of trays, and areinitially located in low positions below the platen. Cages 13 b and 13 dascend from these low positions, unloading trays from the platen afterprinting.

The platen 12 is shown in one of its four possible positions, in whichit spans four of seven equally sized regions of space. The otherpositions are shown by dotted lines 21. The two extreme positions areoutside of the boundary of the cages 13.

The operation of the apparatus will now be described with reference toFIG. 4. The Figure shows the apparatus from a side view, and a tableuseful for understanding the handling and printing process.

Each row of the table represents a different time interval during theprocess. Time passes from the top of the table to the bottom. The firstfour rows represent a start-up sequence for loading and printing thefirst trays, and the bottom four rows represent an end sequence fordealing with the last trays. The middle four rows are repeated for asmany iterations as is necessary for printing the entire batch of slides.

Each column of the table corresponds to a possible position of theplaten. The platen occupies four adjacent positions within the seven.The actual position of the platen at any time is indicated by the shadedportions of the table.

The apparatus is initially set up as follows: the two cages 13 a, 13 bare in their uppermost positions, fully occupied by trays of slides;cages 13 b, 13 d are in their lowest positions, empty. The platen isinitially empty.

First a startup sequence is performed, as represented by rows R1 to R4of FIG. 4:

The platen is positioned as illustrated, occupying the third to sixth ofthe seven regions (counting from the left). The first tray is loadedonto the platen by a downward movement of the right-most cage, cage 13a. As described above, the downward movement of the cage causes the trayto come to rest on the platen, freeing the tray from the ledges of cage13 a and depositing it onto the platen. This action is represented bythe word ‘load’ in the table, underneath the cage in question.

The platen then moves one pitch to the right placing the tray outsidethe frame and ledges of cage 13 a. A second tray is loaded by cage 13 ato a platen position adjacent to the first tray.

The platen then moves three pitches to the left, so that it occupies thefirst to fourth positions. Next, the printhead performs its firstmovement, printing the slides located on the first tray (now locatedunder the printhead rail). This action is represented by the word‘print’ underneath the printhead in the table of FIG. 4 at row R3.

When the printhead has passed the end of the slide tray, the printheadslows down and changes direction. While the printhead is turning round,the platen moves one pitch to the right. The printhead now prints thesecond of the trays, while moving in the reverse direction.Simultaneously, while the printhead is moving but the platen isstationary, the cage 13 c loads a third tray. At the same time, cage 13b unloads the first tray that was printed. This unloading action iseffectively the reverse of the loading action. The cage 13 c surroundsthe tray as it rests on the platen, and the ledges are locatedunderneath the ends of the tray. The cage 13 b moves upwards, so thatthe ledges are brought into contact with the tray, and then lift thetray from the platen. This unloading action is represented in the tableof FIG. 4 is ‘unload’.

The platen moves one pitch to the right, completing the start-upsequence, and the system enters a central sequence that is repeated asoften as is appropriate for the number of trays in the machine.

The central sequence follows the same principle. Cages 13 load andunload trays during printing and when the platen 12 is stationary. Theplaten moves while the printhead is reversing direction. The centralsequence shown, consists of four stages, represented by rows R5 to R8.The apparatus first load 3 two trays 5 from cages 13 a and 13 c, unloadsone tray onto cage 13 b, and prints the tray that is aligned with theprinthead. The following two steps respectively involve a printoperation and the loading of a new tray from cage 13 a, and printoperation and an unloading action onto cage 13 d. The central sequencetherefore prints four trays in four traverses of the printhead. That is,the printhead is busy at every step of the process. The central sequenceis repeated as many times as necessary, until the cages 13 a and 13 care almost empty of trays.

Rows R9 to R12 represent an end sequence for handling the remainingtrays on the platen 12. At R9, the final tray is loaded onto the platenform cage 13 d, the penultimate tray is printed, and a tray is unloadedonto cage 13 b. The next steps involves the printing of the final tray,and the subsequent unloading of the trays onto cage 13 d.

The whole of the above-described operation consists of a start-upsequence, a number n of repeats of the four-stage central sequence, andan end sequence. The operation results in the printing of a set ofliquids held within the printhead onto all 4(n+1) trays of slides in themachine. At the end of this operation the trays have been transferred,with reversal of order, from the two loading cages 13 a, 13 c to the twounloading cages 13 b, 13 d. Cages 13 a, 13 b were initially in a raisedposition, but have now descended below the platen, emptying of trays.Cages 13 b, 13 d, initially below the platen, have ascended filling withtrays.

It is notable that only four out of a total of 4(n+2) operations do notinvolve printing, so the printhead is kept busy with great efficiency,particularly if n is substantial.

When the next set of liquids has been acquired by the printhead, theentire operation is applied in reverse, printing the new set of liquidsonto slightly different positions on all the trays of slides. The loadcages 13 a, 13 c, which were moving downwards, have now become unloadcages moving upwards, and vice versa. The scheme illustrated in thetable of FIG. 4 has the highly desirable property that every tray isprinted with the printhead travelling in the same direction as with theprevious set of liquids. This minimises errors due to the time of flightof the drops, as the shifts will in the same direction for all liquidsprinted onto a given slide. At the end of two complete operations, twosets of liquids have been printed onto all of the slides, and all thecages and trays are back in their original positions.

Multiple sets of liquids are printed using the same overall operation,alternately in the order given in FIG. 4 and in reverse. The positionson the slides of the sets of spots are shifted in the direction ofprinthead motion by applying different offsets to the triggeringelectronics each time the printhead performs a series of traverses.After a number of operations, the slides have been filled with spotsalong the line of travel of the printhead. During the next fewoperations, the four positions visited by the platen, while stillequally spaced at the same pitch, are shifted slightly relative to theprevious ones. This causes another row of spots to be printed on theslides. It is necessary for the entire assembly of four cages to occupya slightly different position for each row of spots. As printing of alarge number of liquids proceeds, multiple rows of spots are produced onthe slides. Their spacing in the direction of printhead travel iscontrolled by the timing of printhead triggering, and the spacingperpendicular to printhead motion is determined by the shifts in platenpositions. Accuracy of spot positioning is guaranteed by the accuracy ofthese two motions and by the mechanism whereby trays stored oninaccurately manufactured cages are located precisely on the platen asthey are loaded.

The sequence in the table of FIG. 4 prints 4(n+1) trays of slides. Ifthe number of trays to be printed is even but not divisible by four,i.e. 4n+2, the sequence shown in the table of FIG. 5 can be used. Thissequence appears to be slightly more efficient than that in the table ofFIG. 4, in that one fewer stage is required at start-up and at the end.However, as explained above, it is highly desirable to guarantee thatindividual slides are always printed with printhead motion in the samedirection. The sequence of FIG. 5 will require an extra traverse by theprinthead at the outset, and at the end in order for the printheadmotion to be consistent.

It is possible to extend these schemes to handle an odd number of traysor to handle the situation where the last tray is not filled withslides. Thus, any number of slides can be handled, not just a multipleof fifty.

Other schemes are possible, involving cages which load more than onetray at a time onto the platen; using two or more than four cages; usingcages to store both unprinted and printed trays.

A practical convenience of the proposed four-cage system is that at theoutset the two cages closest to the front of the machine can be loadedwith trays, and the platen used to transfer the contents of one of themto the rear of the machine as required to start the sequences of FIG. 4.

The present invention provides an efficient means of printing a largenumber of substrates, by providing a rapid means of storing, retrieving,printing and re-storing slides.

The arrangement reduces the requirement for reloading the printhead withdifferent liquids. The liquids are valuable and available in smallquantities only. The loading of liquids into the printhead is inevitablywasteful in that only a proportion of each liquid is usefully printed.Ink jet printheads produce very small drops, so once liquids areintroduced into the printhead, it can print a very large number ofspots. The present invention utilises this characteristic of theprintheads effectively.

A further advantage of the invention arises from reciprocating theprinthead motion using a one-dimensional transport, and mountingmultiple trays on a platen which is capable of movement at right-anglesto the printhead motion. The printhead traverses to print the tray whichis in the appropriate position on the (stationary) platen; then theplaten moves laterally while the printhead is turning round at the endof its stroke, bringing another tray of slides into position underneaththe axis of printhead motion. By the time the next printhead stroketakes place, the platen is again stationary. Accurate spot positioningis achieved in the direction of printhead travel by timing of the dropejection, as disclosed in patent application WO 02/11889, and in theperpendicular direction by precise positioning of the platen.

The invention therefore minimises the time during which the printhead isnot printing.

An additional advantage of this approach is that larger numbers of trayscan be printed than those which fit on the platen: one or more cages canbe used to store the trays when they are not being printed, to feed themonto the platen for printing and to remove them afterwards. A number oftrays can be stored above each other on shelves in each cage; one ormore cages can be moved vertically downwards so as to deposit the traysin turn onto the platen in preparation for printing. One or more othercages, moving vertically upwards, can remove them afterwards. The cagescan perform these functions while the platen is stationary, during theprinting stroke of the printhead. Thus the loading of trays onto theplaten and unloading from it need not add to the time taken to print theoverall number of slides in the machine; this scheme is equivalent inspeed to a system using an impracticably large platen to hold all thetrays.

A further advantage of this approach is that the cages and their motionneed not be precise: if the trays are equipped with location featureswhich engage with matching features on the platen, the act of loadingeach tray onto the platen ensures its accurate positioning with respectto the platen. The only parameters that need to be accurate are theprinthead mounting, its motion, the platen's location features and itsmotion. Both of these motions are one-dimensional.

It will be evident to the skilled reader that various changes could bemade to the above-described embodiments within the scope of theinvention. For example, different numbers of loading and unloading cagescould be employed. In addition, one cage could unload trays, and couldreload the same trays from the platen after printing. A furtherarrangement may utilise two cages that simultaneously unload or load twotrays at different positions on the platen.

Various modifications and improvements can be made within the scope ofthe invention herein intended.

1. Apparatus for transferring substrates to and from a printer,comprising: a first storage unit for storing substrates prior to aprinting operation, the first storage unit having a plurality ofvertically stacked substrate supports; a platen for receiving asubstrate from said first storage unit, aligning the substrate with aprinthead prior to a printing operation, and displacing the substratesubsequent to a printing operation to an unloading position; a secondstorage unit for storing substrates subsequent to said printingoperation, the second storage unit having a plurality of verticallystacked substrate supports; wherein the first and second storage unitsare movable vertically with respect to the platen, and in use, relativevertical movement of the first storage unit and the platen transfers asubstrate from the supports of the first storage unit to the platen, andrelative vertical movement of the second storage unit and the platentransfers a substrate from the platen to the supports of the secondstorage unit.
 2. Apparatus as claimed in claim 1, wherein the verticallystacked substrate supports of the first and second storage units arearranged to support substrate trays for holding a plurality ofsubstrates.
 3. Apparatus as claimed in claim 2, wherein the platenreceives a substrate tray from the first storage unit, the substratebeing held on said substrate tray.
 4. Apparatus as claimed in claim 2,wherein a substrate tray extends lengthways across the width of theplaten, the length of the tray being greater than the width of theplaten.
 5. Apparatus as claimed in claim 1, wherein the first and secondstorage units comprise frames defining an interior cavity, into whichthe platen extends.
 6. Apparatus as claimed in claim 1, furthercomprising third and fourth storage units movable vertically relative tothe platen.
 7. Apparatus as claimed in claim 6 wherein two of saidstorage units are arranged on a first side of the printhead, and two ofsaid storage units are arranged on the opposing side of the printhead.8. A method for printing substrates on a platen, the method comprisingthe steps of: printing a first substrate by imparting linear movement tothe printhead, thereby causing the printhead to traverse the firstsubstrate in a first direction; aligning a second substrate with theprinthead, whilst reversing the direction of motion of the printhead;printing the second substrate by imparting linear movement to theprinthead, thereby causing the printhead to traverse the secondsubstrate in a second direction opposite to the first.
 9. The method asclaimed in claim 8 wherein the substrates are aligned by impartingrelative lateral movement between the platen and the printhead.
 10. Themethod as claimed in claim 8 comprising the additional step oftransferring the second substrate to the platen from a substrate storageunit.
 11. The method as claimed in claim 10 wherein the step oftransferring the second substrate to the platen is carried outsimultaneously with the printing of the first substrate.
 12. The methodas claimed in claim 8 wherein the step of aligning the second substratewith the printhead also aligns the first substrate with a substratestorage unit.
 13. The method as claimed in claim 8 comprising theadditional step of transferring the first substrate from the platen to asubstrate storage unit.
 14. The method as claimed in claim 13 whereinthe step of transferring the first substrate from the platen to asubstrate storage unit is carried out simultaneously with the printingof the second substrate.
 15. The method as claimed in claim 10 whereinthe transfer of a substrate between the platen and the substrate storageunit is carried out by imparting relative vertical movement between asubstrate storage unit and the platen.
 16. A method for printingsubstrates on a platen, the method comprising the steps of: printing afirst substrate whilst simultaneously transferring a further substratebetween the platen and a substrate storage unit; aligning the furthersubstrate with the printhead; printing the further substrate.
 17. Themethod as claimed in claim 16 wherein the first substrate is printed bycausing the printhead to traverse the substrate in a first direction,the further substrate is printed by causing the printhead to traversethe further substrate in a second direction opposite to the first, andthe step of aligning the further substrate with the printhead is carriedout whilst reversing the direction of motion of the printhead.
 18. Themethod as claimed in claim 16 wherein the step of aligning the furthersubstrate with the printhead also aligns the first substrate with asubstrate storage unit.
 19. The method as claimed in claim 16 whereinthe substrates are aligned by imparting relative lateral movementbetween the platen and the printhead.
 20. The method as claimed in claim16 comprising the additional step of transferring the first substratefrom the platen to a substrate storage unit.
 21. The method as claimedin claim 20 wherein the step of transferring the first substrate fromthe platen to a substrate storage unit is carried out simultaneouslywith the printing of the further substrate.
 22. The method as claimed inclaim 16 wherein the transfer of a substrate between the platen and thesubstrate storage unit is carried out by imparting relative'verticalmovement between a substrate storage unit and the platen.
 23. A methodfor printing substrates on a platen, the method comprising the steps of:printing a substrate by imparting linear movement to the printhead,thereby causing the printhead to traverse the substrate in a firstdirection, whilst simultaneously transferring a further substratebetween the platen and a substrate storage unit; aligning the furthersubstrate with the printhead while reversing the direction of motion ofthe printhead; printing the further substrate by imparting linearmovement to the printhead, thereby causing the printhead to traverse thesubstrate in a second direction opposite to the first.
 24. The method asclaimed in claim 16 wherein the substrates are mounted on substratetrays.
 25. The method as claimed in claim 24 wherein the first substrateis one of a set of substrates mounted on a first substrate tray, and thesecond or further substrate is one of a set of substrates mounted on asecond substrate tray.
 26. The method as claimed in claim 24 wherein thetransfer of substrates to or from the platen is by transfer of substratetrays to or from the platen.
 27. The method as claimed in claim 16,wherein the steps of the method are repeated for third and additionalsubstrates or substrate trays.